Method of finishing sheet pyroxylin



\N N W R 1 1 1 I I I I I I 1 I 1 i m m f N km mm NW RN NN METHOD OF FINISHING SHEET PYROXYLIN 3 D W Wm MN New. 6, 1934 Patented Nov. 6, 19 34 eia-162 METHOD or mrrsnmc sneer rmoxrmz Robert G. OKane and Elmer B. Derby, Springfield, Mass., assisnors to The Flberloid Cor-' poratlon, Indian Orchard, Mass., a corporation of Massachusetts Application February 12, 1930, Serial No. 427,780

14 claims.

Our present invention relates to a method of making and finishing pyroxylin sheets of the general character used in the manufacture of laminated or non-shatterable glass. In general the tobject of the invention is to improve the process of making such sheets from a plastic mass of pyroxylin gell by extrusion which process was invented by Gustavus J. Esselen, J12, and is de= scribed in an application for Letters Patent filed it by him November 1, 1929, Serial No. 404,633, and to make possible the finishing of said sheets as a part of a continuous process of which the extrusion forms a part and without resorting to sccalled plate polishing.

In the process described in the said application of G. J. Esselen, Jr., pyroxylin in the form of a colloidal gell of the stiffness of bread dough is forced under exceedingly heavy pressure through an orifice and is thus formed into a web which 20 while still soft and containing a considerable proportion of solvent is nevertheless self-sustaining and capable of being handled.

The process embodying our invention makes it possible to finish progressively a continuous web of pyroxylin and to produce a product equal to or better than that heretofore produced, without resorting to any treatment of individual sheets as heretofore.

The importance of the present invention will be apparent when the old method of producing polished pyroxylin sheets is considered. In this process the usual mix of nitrocellulose, camphor and alcohol was, after being rolled on hot rollers, formed into a cake of the size of the sheet by 3 pressing it in a suitable mold in a hydraulic press; it was sliced into sheets in a slicing machine or planer, then the sheets were hung up separately in dryers and cured for some days, and finally if desired each sheet was pressed between polished steel sheets in hot hydraulic presses. The entire process took from ten days to two weeks, the amount of stock in process, the space required and the equipment were all very large. The equipment included thousands of nickel plated steel press plates each of which had to be polished to the perfection of plate glass.

When the making of sheets by the Esselen extrusion process was first conceived, it was thought that this would do away with plate polishing but it was found that although the web could be produced in this way and was admirably adapted to certain purposes, it was apt to be uneven in thickness or gauge, wrinkled or curly and with a dull lustreless surface and therefore that it was neces sary to polish and flatten it. It was attempted to do this by calendar rolls but this did not prove altogether successful and resort to plate polishing with all its expense and objections appeared so to be necessary.

Our present invention does away with plate polishing or calendaring, and produces a satisfactory surface on a continuous web of material, and therefore when operated in connection with the Esselen extrusion process realizes the hope of a continuous process for the production of a finished and cured sheet of material without requiring any operations to be performed on individual sheets. Since the process is continuous and the curing takes place as the g is done and the complete sheet is produced in less than twen ty-four hours-usually less than twenty-from the time the mix is made, the amount of stock in process is but a small fraction of that in the cake process and the expense for equipment and storage space is also small. I

' Our present invention is based on the discovery that when a sheet of pyroxylin mix .of proper chemical and physical character is stretched (i. e. elongated in any or all directions) before being cured (i. e. while still containing a certain proportion of solvent) and before its physical structure is modified by the removal of the solvent,

a striking change takes place in the appearance of the surface of the sheet which we believe to be due to a change in the arrangement of the particles or molecules particularly those on the surface; and, further, that, if suilicient solvent is removed while the sheet is held under tension, the character of the surface becomes permanent. The exact nature of the change is uncertain but its existence will be at once apparent to one who observes the change in appearance which the surface of the sheet undergoes as it is being stretched. In this connection, it is to be observed that a pressure of some hundreds of pounds to the square inch is necessary to force the mass through the orifice to form the sheet, that the pyroxylin is somewhat compressible and therefore expands when the pressure is suddenly released as the web emerges from the orifice, that the different parts of the mass may flow at different speeds as it passes through the orifice, that the mass contains a considerable amount of solvent (about 30 to 40 per cent. by weight) and that the solvent is rapidly extracted from the mass. All of these .factors and perhaps others afiect injuriously to a greater or less extent the uniformity of the sheet and the character of its surface.

We are aware that it has been proposed to remove wrinkles from sheet pyroxylin by holding it flat under tension while it dries, but it was not known that stretching while the material was still soft and plastic and removing the solvent would improve the appearance and surface of the stock especially when the stretching was done in connection with the proper application of hot air to the surface, nor was any attempt made to take advantage of these facts to produce a finished sheet particularly an extruded web made by a continuous process.

Our present invention is, we believe, chiefly applicable to what we term the dry process in which the solvent is removed by evaporation, but we believe it to be also applicable to some extent to the wet process in which the plastic pyroxylin is extruded directly into a. bath by which the pyroxylin is hardened.

In the dry process the application of hot air to the pyroxylin as the stretching takes place forms an important feature of the invention. It is important that the air be heated to the right temperature to keep the outside of the sheet plastic so that it will not crack or break under the stretching and also to prevent blushing i. e. clouding the surface which takes place if the air is too cool, due, we believe, to the effect of condensed moisture which will take place whenever the surface temperature of the sheet falls below the dew point.

We believe our present invention to be an important and fundamental one since we are first to produce a finished and polished sheet of pyroxylin by the method described, and therefore we do not intend to limit our claims except as expressly stated therein.

In the drawing:

Fig. 1 is a longitudinal section of an apparatus suitable for practicing the invention embodying our present invention as applied to the production of sheet pyroxylin by the dry process.

Fig. 2 is a plan view of the apparatus shown in Fig. 1.

Fig. 3 is a detail perspective view of the nozzle or die.

Fig. 4 is a detail perspective view of a modified form of the nozzle or die.

It will be understood that this apparatus is shown only by way of illustration and that we do not limit ourselves to its use since other types of apparatus may be more satisfactory under certain conditions also, that in the present application for Letters Patent we do not claim the patentable features of the said apparatus as they form the subject matter of another application.

Referring to the drawing.

At 11 is shown a mixer of standard form such as is generally used in preparing a suitable mix. Such a mix may be one such as is now commonly employed in the cake process, the chief ingredients being a suitable cellulose ester, such as nitrate acetate, or formate, etc. or the equivalent for the purpose in question; camphor, either natural or synthetic or some other suitable plasticizer and a solvent for the particular material employed, also if desired a stabilizer such as urea. Solely as an illustration of the ingredients of one suitable mix, the following formula is given:

Pyroxylin (dry weight) 210 pounds Camphor 70 pounds Alcohol 175 pounds Urea 17 ounces doughy consistency, somewhat stiffer than bread dough.

From the mixer 11,.the mix is discharged into a suitable hydraulic filter press having an hydraulic cylinder 12, and a working cylinder 13 and is forced through a suitable filtering medium for instance an eight ounce duck as indicated at l. After passing the filter, the mass passes into a feed cylinder 15 containing a feed screw 16 by which it is forced into the extrusion press 17. In practice we have used for this purpose a screw extruder and find-that it produces a sufficiently uniform feed and pressure at the nozzle. The extruder 1'? is provided with a nozzle or die '18 containing an orifice 19 (see Fig. 3) which in the machine shown in the drawing is circular and produces a tubular sheet which is split by a knife 20 to form the web A. It will be understood that we do not limit ourselves to a circular orifice since a straight one 50 (see Fig. 4) may be used with equal success. After leaving the nozzle 18 and being slitted by the knife 20, the sheet or web A is led over rolls 21 which open out the sheet and hold it flat. After passing the rolls 21 the web or sheet passes a series of rollers 22 to form a series of vertical festoons and thence to a driven roller 23 preparatory to entering a drier 32. At some point between the rollers 21 and the driven roller 23 a festoon is formed in which is supported a floating roller 24. The roller 23 is driven at a surface speed which is greater than that of the stock at the nozzle and with the floating roller 24 maintains a continuous tension on the stock at all points between the driving roll 23 and the nozzle or die 18. The mechanism thus described pulls the web forward from the nozzle at a speed greater than that at which it would otherwise be extruded from the orifice and thus stretches the web all the way between the drive roll and the nozzle. This is an important feature of our invention as we find that stretching at this point tends to remove the unevennesses which result from some of the factors already mentioned and possibly others. At 25 and 26 are shown hot air pipes through which hot air driven by the fans 27 and 28 is discharged against the surface of the web just as it emerges from the orifice. This feature also contributes materially to the success of our invention as the hot air evaporates and carries off the volatile solvent as it leaves the surface of the sheet and helps to bring the pyroxylin into proper condition for subsequent treatment. Furthermore being hot, it evaporates the solvent more rapidly, keeps the surface plastic, and keeps the temperature above the dew point so that blushing does not occur. From the rollers 23 the web passes into a dryer 32. In this dryer the air is heated and maintained at the proper temperature to remove the required amount of solvent before it emerges. On emerging it (the ribbon) passes around a guide roll 51. The roll 52 is another floating roll which maintains the proper tension in the dryer.

After leaving the drying chamber 32, the sheet or web A is subjected to transverse stretching in some suitable device. For this purpose we employ a specially constructed tenter 40 provided with two longitudinal and slightly diverging series of movable nippers 34 carried by endless chains 35 which diverge. The divergence of the chains is very slight (it has been exaggerated in the drawing for cleamess of illustration) but the tenter is of considerable length so that the sheet is given a very slow powerful progressive transverse stretching as it travels through the tenter 40. At

the same time a series of nozzles 37 blow hot air on both sides of the work. This hot air both removes the solvent and keeps the surface of the web from hardening to such an extent that it would break under the stretching to which it issubjected.

By the time the web leaves the tenter 40, its surface takes on an altogether different appearance from that of a piece of extruded sheet which has not been subjected to this finishing process. The surface of the web is smooth and glossy and though of an appearance somewhat different from that of a plate polished sheet is as satisfactory for most commercial uses. The gauge is surprisingly uniform, and the sheet has the great advantage that the flatness of the surface is permanent, there being no sheeter lines which will re-appear after being vaporized as is the case with sheets made by the cake process and plate polished.

After leaving the tenter'40, the web passes through a suitable final dryer or seasoning chamber 38 where more solvent is removed until the residue is brought down to the amount which is usually to be found in material of this character. Thereafter the web can be cut into individual sheets.

From the foregoing it will be seen that our invention provides a continuous process by which a plastic mass of pyroxylin mix of the kind suitable for the cake process can be made into finished sheets without performing any operations on individual sheets, and that the process can be completed in the time required for the web to travel through the apparatus, which in practice with the particular mix and apparatus which we have employed is not over twenty hours. The process also has the very great advantage that it makes possible the production of sheets of different sizes by the same equipment with a minimum of loss, it being possible to accomplish this by changing the nozzle of extruding press to produce a wider or narrower sheet, making suitable adjustments in the extruder, and adjusting the tenter accordingly. With the cake process on the other hand, the size of the sheets which can be produced is limited by the size of the cake moulds and presses, of the sheeters, and of the polishing presses, so that only one size of sheets can be made economically with a given equipment.

We claim:

1. That improvement in theart of producing smooth pyroxylin sheets which consists in forming pyroxylin gel into a plastic self-sustaining sheet and while it is still in plastic condition due to the presence of included solvent altering the physical condition of the surface of the sheet by stretching it longitudinally and transversely.

2. That improvement in the art of making sheet pyroxylin which consists in altering the physical condition of the sheet while still containing a solvent by stretching the sheet longitudinally and transversely while the sheet is still of the surface of the sheet by stretching it while the sheet is still plastic.

4. The method. of producing sheet pyroxylin which consists in extruding through an orifice, a sheet of pyroxylin gel containing a solvent, altering the physical condition of the surface of the sheet by stretching it and at the same time extracting a part at least of the solvent.

5. That improvement in the art of making sheet pyroxylin which consists in extruding through an orifice a plastic sheet of pyroxylin gel and subjecting the sheet thus formed to tension at the orifice.

6. That improvement in the art of making sheet pyroxylin which consists in extruding through an orifice a sheet of pyroxylin gel which is rendered plastic by the presence of a solvent, subjecting the sheet to tension at the orifice and extracting a part at least of the solvent while the sheet is still under tension.

7. The method of producing sheet pyroxylin which consists in extruding through an orifice w a sheet of pyroxylin gel containing a solvent, maintaining the surface of the sheet in plastic condition and extracting a part at least of the included solvent by blowing hot air on the sheet, and simultaneously therewith altering the physical condition of the sheet by stretching it.

8. The method of producing sheet pyroxylin which consists in extruding through an orifice a sheet of pyroxylin gel containing a solvent, subjecting the sheet to tension at the orifice and simultaneously blowing hot air on it, and then subjecting the sheet to transverse stretching.

9. The method of producing sheet pyroxylin which consists in extruding through an orifice a sheet of pyroxylin gel, and then subjecting the a sheet to progressive transverse stretching.

10. The method of producing sheet pyroxylin which consists in extruding through an orifice a sheet of pyroxylin gel containing a solvent, subjecting the sheet to tension at the orifice and simultaneously blowing hot air on it, and then while the sheet is still in plastic condition subiecting it to progressive transverse stretching.

11. That improvement in the art of making sheet. pyroxylin which consists in extruding through an orifice a plastic mass to form a web and then altering the physical condition of the web .by stretching it while the material is still plastic.

12. The method of producing sheet pyroxylin which consists in extruding through an orifice a mass of pyroxylin gel containing a solvent, subjecting the web to tension at the orifice and 139 simultaneously blowing hot air on it and then while the web is still in plastic condition subjecting it to progressive transverse stretching.

13. The method of producing sheet pyroxylin which consists in extruding through an orifice a. sheet of pyroxylin gel and then subjecting the sheet to longitudinal and transverse stretching.

14. The method of producing sheet pyroxylin which consists in extruding through an orifice a plastic mass in the form of a sheet, then altering the physical condition of the surface of the sheet by stretching it while the sheet is still plastic and then hardening the sheet while it is still held under tension.

ROBERT G. OKANE.

ELMER R. DERBY. 

